JavaScript：TypeError：无法读取未定义的属性“0”

Question

for 循环给我一条错误消息“TypeError：无法读取未定义的属性'0'”我该如何解决这个问题？

 const ticker = () => "msn"; // crypto price data for multiple crypto currencies function crypto2() { var x = ticker().slice(0, 50); console.log("x = " + x); console.log("ticker length = " + x.length); var urlA = "https://min-api.cryptocompare.com/data/pricemulti?fsyms=" + x + "&tsyms=USD&limit=300"; var result = null; $.ajax({ url: urlA, async: false, // makes a synchrously data call to cryptocompare dataType: "json", success: function(data) { result = data; } }); var y = result; console.log("y = " + JSON.stringify(y)); console.log("y.BTC = " + y.BTC.USD); console.log("rght = " + JSON.stringify(x[0])); var D1 = []; for (var i = 0; i < 40; i++) { D1.push(yx[i].USD); } // console.log("data = " + D1); return D1; } crypto2()

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Answer 1

你没有x[0]也没有y.BTC.USD

您可以使用此语法

D1.push(y?.x?.[i].USD);

但我会使用 map

 const ticker = () => ["eth","doge","btc"]; // crypto price data for multiple crypto currencies function crypto2() { var x = ticker().slice(0, 50); console.log("x = " + x); console.log("ticker length = " + x.length); var urlA = "https://min-api.cryptocompare.com/data/pricemulti?fsyms=" + x + "&tsyms=USD&limit=300"; var result = null; $.ajax({ url: urlA, async: false, // makes a synchrously data call to cryptocompare dataType: "json", success: function(data) { result = data; } }); console.log("result = " + JSON.stringify(result)); const D1 = Object.keys(result).map(key => result[key]?.["USD"]) return D1; } console.log(crypto2())

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和异步

 const ticker = () => ["eth","doge","btc"]; // crypto price data for multiple crypto currencies function crypto2() { var x = ticker().slice(0, 50); console.log("x = " + x); console.log("ticker length = " + x.length); var urlA = "https://min-api.cryptocompare.com/data/pricemulti?fsyms=" + x + "&tsyms=USD&limit=300"; var result = null; $.ajax({ url: urlA, dataType: "json", success: function(data) { const D1 = Object.keys(data).map(key => data[key]?.["USD"]) console.log(D1); } }); } crypto2()

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